The present invention generally relates to circuit board apparatus, and more particularly relates to apparatus and methods for cooling of integrated circuit (IC) packages mounted on circuit boards.
Under the conventional method by which integrated circuits are hermetically packaged, an internal cavity is formed within a multi-tiered substrate structure, typically of a ceramic material, and opens outwardly through a bottom side of the substrate structure. A die is then mounted on an upper side surface portion of the cavity and wire bonded to the various circuitry tiers of the substrate structure. After the die is operatively mounted in the cavity, the cavity is filled with an inert gas, such as nitrogen, and hermetically sealed using a lid member received in the bottom side cavity opening of the substrate structure. The completed IC package is then mounted, lid side down, on a side of a circuit board and appropriately connected to the board circuitry, for example by pins mounted on the substrate structure and inserted into corresponding holes in the circuit board.
Since the ceramic material of the IC package substrate structure has a considerably higher thermal conductivity than the inert gas within the die cavity, most of the die operational heat conducted outwardly through the balance of the IC package is conducted upwardly through the substrate portion directly above the die--only a relatively small amount of heat is conducted downwardly through the IC package. To facilitate the removal of this upwardly conducted heat, it is customary to mount a heat sink device on the top side of the IC package substrate. Typically, these heat sinks must be provided with large surface areas and accordingly undesirably impose constraints on already complex system cooling problems--for example within a computer housing in which the IC package/circuit board structure is mounted.
As can readily be seen from the foregoing, it would be highly desirable to provide improved apparatus and methods for more effectively removing operational heat from an IC package mounted on a side of a circuit board. It is accordingly an object of the present invention to provide such improved heat removal apparatus and methods.